Problem selecting to children of the same parent

I have this taxonomy schema and I'm using Hierarchical Select Taxonomy:

-term1
-term2
  -child1
  -child2

I select term2 and the second dropdown selection appear, I use dropbox to add child1.
Now I want to add child2, so I select again term2 but nothing happens. I have to select term1, then term2, the dropdown appears and I can choose child2.
It's not a big bug, but it can create some confusion especially if the user don't know this.
I hope you understand my explanation, if you need more details I can provide them, maybe taking some screenshots.